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<body>
<h1 id="-12-">第12章 流向的改变</h1>
<h1 id="-direction-">改变水平流向的<code>direction</code></h1>
<h2 id="-direction-"><code>direction</code>简介</h2>
<ul>
<li><code>direction:ltr;</code> 默认值</li><li><code>direction:rtl;</code></li></ul>
<p><code>direction</code>属性可以改变替换元素或者<code>inline-block/inline-table</code>元素的水平呈现顺序。</p>
<ul>
<li><code>direction</code>属性可以让单行文字溢出用<code>...</code>显示。</li><li><code>direction</code>属性可以改变表格中列的呈现顺序。</li><li><code>direction:rtl;</code>可以让<code>text-justify</code>两端对齐元素，最后一行落单的元素右对齐显示。</li></ul>
<h2 id="-direction-unicode-bidi-"><code>direction</code>的黄金搭档<code>unicode-bidi</code></h2>
<p><code>unicode-bidi</code>兼容性比较好的属性：</p>
<ul>
<li><code>unicode-bidi:normal;</code> 默认值</li><li><code>unicode-bidi:embed;</code></li><li><code>unicode-bidi:bidi-override;</code></li></ul>
<ol>
<li><code>unicode-bidi:embed;</code>只能作用在内联元素上。<code>embed</code>属性值的字符排序是独立内嵌，不受外部影响。</li><li><code>embed</code>属性值的作用原理是在元素的开始和结束为止插入特殊字符实现，在元素开始位置添加了一个<code>U+202A</code>字符（<code>direction:ltr</code>）或<code>U+202B</code>字符（<code>direction:rtl</code>），并在该元素结束位置添加一个<code>U+202C</code>字符。</li><li><code>bidi-override</code>：重写双向排序规则。</li></ol>
<h1 id="-writing-mode-"><code>writing-mode</code></h1>
<h2 id="-writing-mode-"><code>writing-mode</code>原来的作用</h2>
<p><code>writing-mode</code>用来实现文字竖向呈现。</p>
<p><strong>1. <code>writing-mode</code>的语法</strong></p>
<p>CSS3语法：</p>
<p><strong>关键字</strong></p>
<ul>
<li><code>writing-mode: horizontal-lab</code> 默认值</li><li><code>writing-mode: vertical-lr</code></li><li><code>writing-mode: vertical-rl</code></li></ul>
<p><strong>全局值</strong></p>
<ul>
<li><code>writing-mode: inherit</code></li><li><code>writing-mode: initial</code></li><li><code>writing-mode: unset</code></li></ul>
<p>IE关键字：</p>
<ul>
<li><code>lr-tb</code>：内容从左往右、从上往下水平流动，并且下一行水平元素在上一行元素的下面，所有符号都是直立定位。</li><li><code>rl-tb</code>：内容从右往左、从上往下水平流动，并且下一行水平元素在上一行元素的下面，所有符号都是直立定位。</li><li><code>tb-rl</code>：内容从上往下、从右往左垂直流动，下一行垂直定位于前一个垂直行的左边，全角符号直立定位，非全角符号顺时针方向<code>90°</code>。</li><li><code>bt-rl</code>：内容从下往上、从右往左垂直流动，下一行垂直定位于前一个垂直行的左边，全角符号直立定位，非全角符号顺时针方向<code>90°</code>。</li><li><code>bt-lr</code>：内容从上往下、从左往右垂直流动，下一行垂直行在前一个的左边`。</li><li><code>tb-lr</code>：内容从下往上、从左往右垂直流动。</li><li><code>lr-bt</code>：内容从下往上、从左往右水平流动，下一行水平行在前一个的上面`。</li><li><code>rl-bt</code>：内容从下往上、从右往左水平流动</li></ul>
<p><strong>补充说明</strong>：相同的<code>writing-mode</code>属性值不会叠加。</p>
<p><strong>2. 需要关注的<code>writing-mode</code>属性值</strong></p>
<ul>
<li><code>writing-mode: lr-tb | tb-rl | tb-lr (IE8+)</code></li><li><code>writing-mode: horizontal-tb | vertical-rl | vertical-lr</code></li></ul>
<h2 id="-writing-mode-"><code>writing-mode</code>改变了哪些规则</h2>
<p><code>writing-mode</code>将页面默认的水平流改为垂直流。</p>
<p><strong>1. 水平方向也能<code>margin</code>合并</strong></p>
<p><strong>2. 普通块元素可以使用<code>margin:auto</code>实现垂直居中</strong></p>
<ol>
<li>图片元素</li><li>普通块状元素</li></ol>
<p><strong>3. 可以使用<code>text-align:center</code>实现图片垂直居中</strong></p>
<p><strong>4. 可以使用<code>text-indent</code>实现文字下沉效果</strong></p>
<p><p data-height="265" data-theme-id="0" data-slug-hash="oMaqXb" data-default-tab="css,result" data-user="whjin" data-pen-title="`text-indent`实现文字下沉效果" class="codepen">See the Pen <a href="https://codepen.io/whjin/pen/oMaqXb/"><code>text-indent</code>实现文字下沉效果</a> by whjin (<a href="https://codepen.io/whjin">@whjin</a>) on <a href="https://codepen.io">CodePen</a>.</p></p>
<script async src="https://static.codepen.io/assets/embed/ei.js"></script>

<p><strong>5. 可以实现全兼容的<code>icon fonts</code>图标的旋转效果</strong></p>
<p><strong>6. 充分利用高度的高度自适应布局</strong></p>
<h2 id="-writing-mode-direction-"><code>writing-mode</code>和<code>direction</code>的关系</h2>
<blockquote>
<p><code>writing-mode</code>、<code>direction</code>和<code>unicode-bidi</code>是CSS中三大可以改变文本布局流向的属性，其中<code>direction</code>和<code>unicode-bidi</code>经常一起使用，也是仅有的两个不受CSS3的<code>all</code>属性影响的CSS属性，基本上就是和内联元素一起使用。</p>
</blockquote>

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